1. Field of the Invention
The present invention relates to an apparatus for measuring intraocular substances by irradiating an eyeball with an excitation light beam from an excitation optical system and detecting measuring light components including at least either scattered light or fluorescence generated from the eyeball by a photoreceiving optical system.
2. Description of the Background Art
Vitreous fluorophotometry (VFP) is performed as an examination of quantitatively testing the function of a blood-ocular barrier by measuring intraocular fluorescence as a method of irradiating the eyeball with excitation light and obtaining information from scattered light or fluorescence from the eyeball.
In order to diagnose diabetes mellitus or judge necessity for insulin administration, blood-sugar level must be measured. Although a method of collecting blood for measuring the blood-sugar level is correct, this causes the patient pain, and the examination is troublesome and requires a long time.
Therefore, various methods of noninvasively measuring intraocular substances on the basis of optical information from eyeballs are studied. For example, methods of irradiating eyeballs with excitation light and measuring the blood-sugar levels on the basis of information obtained therefrom are studied. One of such methods is a method of irradiating the crystalline lens with excitation light, receiving back-scattered light thereof, separating the same into fluorescence and Rayleigh light through a spectroscope or a dichroic beam splitter, obtaining information allowing diagnosis of diabetes mellitus from a value obtained by normalizing the fluorescence intensity with the Rayleigh light intensity, and diagnosing diabetes mellitus, cataract or still another disease on the basis thereof (refer to U.S. Pat. No. 5,203,328).
In another method, infrared absorption by the crystalline lens or the refractive index of visible light is measured for obtaining the blood-sugar level in the crystalline lens on the basis thereof (refer to Japanese Patent Laying-Open Gazette No. 51-75498 (1976)). In still another method, aqueous humor filling up a clearance between the cornea and the crystalline lens is irradiated with plane polarized light so that the blood-sugar level is obtained by measuring the angle of rotation of the polarization axis or the refractive index (refer to U.S. Pat. No. 3,963,019).
A method of obtaining a cholesterol value as another vital substance is also proposed. In this method, aqueous humor is irradiated with excitation light, so that the intensity of scattered light therefrom or the mobility of protein which is a scatterer is measured for obtaining the cholesterol value (refer to U.S. Pat. No. 4,836,207).
Obtained information varies with the measured eyeball portion such as the vitreous body, the crystalline lens, the aqueous humor or the cornea. In order to obtain information from positions of the eyeball having different depths, therefore, an optical system is so scanned that places for generating fluorescence etc. to be received move along the depth direction of the eyeball (refer to "Ringan" Vol. 38, No. 11, 1195-1199 (1984)).
When the optical system is scanned for measurement for obtaining information from eyeball positions having different depths and the eyeball moves during the scanning, the depths of the measured portions are also changed and no correct measurement can be performed.
Further, the optical system is disadvantageously complicated and increased in size due to the scanning.